over thinking or possibly pregnant?

I've been on the depo shot (birth control shot) for 2 years now. and I know there's only a 1% chance of getting pregnant. but every time im due for another shot, I start my period right away, but this past shot, i didnt get my period and i didnt think anything of it cause the depo shots have stopped me from having periods except when im due for another. but after reading all these pregnancy scare posts I think im starting to get paranoid. I just need reassurance that I'm being paranoid. I would like to finish college first and have a career before being pregnant.